hi there gypsy, i am not an expert but it sounds like it would be more like PCOS than endo causing the length of your periods. you may want to put your post here in the endo/PCOS area to get a bit more help from the others with more knowledge on the site.
that isn't to say you don't have endo but normally only a laparoscopy can identify whether you have it (i hope you don't). good luck